Brushless motors are used in a variety of different implementations, for example for controlling automotive and/or robotic movement of an electromechanical device. Three-phase brushless motors are particularly useful, since they can provide reliable and smooth running.
While it is possible to design an electromechanical device using one or two brushless motors, some mechanical implementations seek further degrees of freedom, for which further such motors may be required. A mechanical implementation using three brushless motors is the subject of the present disclosure, but the reader will appreciate that this does not place a limitation on the disclosure.
Field oriented control (FOC) is a commutation technique used for controlling brushless motors. It is well known that FOC can be computationally intensive. FOC of a brushless motor can be achieved through the use of a digital signal processor (DSP).
Existing DSPs enable control of up to two brushless motors. This limitation takes account of the fact that, in many implementations, other tasks may arise in a mechanical device which require control. The processing capability of the provided DSP will generally be the most effective way of carrying out these additional control tasks. As such, the DSP will not be wholly devoted to FOC of motors.
This limitation on the capabilities of the DSP takes two forms. Firstly, the capacity of the DSP to execute software instructions will, inevitably, have a limit. It has been found that FOC of three brushless motors, within the bounds of present-day DSPs, may exceed this limit. Secondly, DSPs can generally only drive a finite number of outputs. If a motor is driven by pulse wave modulation (PWM) signals, normally six PWM drive signals are required per motor. Driving three brushless motors will thus impose a requirement for drive signals which can be greater than the number of outputs capable of being driven by a DSP.
Furthermore, in many electromechanical applications, there is a desire for miniaturisation. One approach to the above limitations imposed by a DSP, is to provide more than one DSP per controller. However, If a plurality of DSPs is required in order to control electromotive components of the device, miniaturisation can be, at best, incomplete.